fix(analytics): OAuth kayıtlarında Google Ads sign-up conversion'ı ateşle

Conversion sadece register.tsx email path'inde ateşleniyordu; Google OAuth
signup'lar (register + login Google butonu) hiç ateşlemiyordu → ölçüm: paid-
kaynaklı kayıtların ~%79'u OAuth, Google Ads'e görünmüyordu, Max Conversions
sinyalsiz optimize ediyordu. Evrensel post-auth bileşeni (google-ads-signup-
conversion.tsx, __root'a mount) yeni kullanıcıda (createdAt < 30dk) conversion'ı
bir kez ateşler; transaction_id signup_<userId> Google tarafında dedup eder,
register.tsx guard'ı email path'in çift-ateşini önler. _gcl_aw cookie OAuth
roundtrip'inde korunduğu için atıf doğru. Playwright 6/6.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/web/src/components/google-ads-signup-conversion.tsx

@@ -0,0 +1,59 @@
+import { useAuth } from "@/hooks/use-auth";
+import { trackGoogleAdsConversion } from "@/lib/google-ads";
+import { useEffect, useRef } from "react";
+
+/**
+ * Universal post-auth Google Ads sign-up conversion.
+ *
+ * The register page fires the sign-up conversion only on the EMAIL path
+ * (register.tsx). Google OAuth signups — both the register-page Google button
+ * and the login-page Google button — complete server-side after a redirect and
+ * never fire it, so Google Ads saw ~0 of them (measured: ~79% of paid-driven
+ * signups were OAuth → invisible to Google Ads, starving Max Conversions of its
+ * signal). This mounts at the root and fires for any brand-new authenticated
+ * user, covering every signup path.
+ *
+ * Double-count safety: the conversion carries transaction_id `signup_<userId>`,
+ * which Google dedupes on — so an email signup that already fired on the
+ * register page counts once even though this fires again. The localStorage guard
+ * additionally stops repeat fires across the new user's first-session pageviews;
+ * register.tsx sets the same guard so email signups skip the redundant fire.
+ *
+ * Attribution: gtag's own `_gcl_aw` cookie (set from gclid on the ad landing)
+ * survives the same-domain OAuth round-trip, so firing here still attributes to
+ * the original click. Organic (non-ad) new users fire too, but Google only
+ * counts conversions it can tie to an ad click — the rest are ignored.
+ */
+const NEW_USER_WINDOW_MS = 30 * 60 * 1000;
+
+function guardKey(userId: string): string {
+  return `sase-ga-signup-conv-${userId}`;
+}
+
+export function GoogleAdsSignupConversion() {
+  const { user, isLoading } = useAuth();
+  const firedRef = useRef(false);
+
+  useEffect(() => {
+    if (isLoading || !user || firedRef.current) return;
+    const createdAt = user.createdAt ? new Date(user.createdAt).getTime() : 0;
+    // Only genuinely fresh accounts — this is a signup conversion, not a login.
+    if (!createdAt || Date.now() - createdAt > NEW_USER_WINDOW_MS) return;
+
+    const key = guardKey(user.id);
+    try {
+      if (localStorage.getItem(key)) return;
+      localStorage.setItem(key, "1");
+    } catch {
+      // localStorage unavailable — firedRef still prevents in-session repeats.
+    }
+    firedRef.current = true;
+
+    trackGoogleAdsConversion(import.meta.env.VITE_GOOGLE_ADS_SIGNUP_LABEL, {
+      transactionId: `signup_${user.id}`,
+      email: user.email,
+    });
+  }, [user, isLoading]);
+
+  return null;
+}